1. Field of the Invention
The present invention relates to recording medium playing apparatus, such as a disc player for playing a video disc or a digital audio disc.
2. Description of Background Information
There has been proposed a system for recording and reproducing picture information in the form of the subcode, on and from a digital audio disc having a diameter of 12 cm, generally called compact disc (abbreviated as CD hereinafter). The subcode is made up of eight subcode bits, and bit groups forming the subcode are divided into eight channels denoted by letters P, Q, R, S, T, U, V, and W respectively. In the method in which the picture information is recorded and reproduced in the form of the subcode, data corresponding to picture information is configured such that a symbol is formed by 6 bits of channels R through W from among the 8 bits forming the subcode, and 98 symbols are treated as one block, as illustrated in FIG. 1. Two symbols in the 98 symbols are used as a sync signal, and 24 symbols obtained by dividing the remaining 96 symbols by four are treated as a minimum unit of data, i.e. a "pack", which constitutes one instruction of the picture processing.
More specifically, the first symbol (referred to as symbol 0 hereinafter) of the 24 symbols shows one of several modes. A symbol 1 following this symbol 0 is "instruction" which indicates the sort of the instruction. Symbols 2 and 3 following the symbol 1 constitute a parity Q which is an error correction code. Symbols 4 through 19 following the parity Q constitute a data field, and include information such as color information. Finally, symbols 20 through 23 following the data field constitute a parity P which is an error correction code for protecting the information in the "pack".
On the other hand, there are four modes, i.e. "zero mode", "line-graphics mode", "TV-graphics mode", and "user's mode". The "zero mode" is provided for a case where no operation is required for pictures on the display screen, that is, pictures are to be maintained as they are, and all data in the "pack" are 0 for this mode.
The "line-graphics mode" is provided for such a case that a liquid crystal display is provided on the front face of the player, to display notes such as an explanation of a music selection. As shown in FIG. 2, a picture area elongated sideways is formed by pixels which are arranged in 288 columns and 24 rows. In other words, each row includes 288 pixels and each column includes 24 pixels. The term "pixel" means the minimum display element of a picture, and it is general that the picture processing is performed by using picture composing units designated as "fonts" each of which is made up of pixels divided into 6 columns and 12 rows.
The number of "fonts" which can be displayed in the "line-graphics mode" is 48 in the lateral direction, and 2 in the column direction, and this area is designated as "screen area". For providing the scroll function, a line of "fonts" is added to the upper and lower outer peripheries and the right and left peripheries of the "screen area", to form a picture area having 50 "fonts" in the row direction, and 4 "fonts" in the column direction. The subcode is formed so that the picture processing is performed by using a memory having addresses each corresponding to each pixel in this picture area. In addition, the area outside the "screen area" is designated as "border".
The "TV-graphics mode" is a mode for displaying images on the TV screen, and a picture is formed by pixels arranged in 192 rows and 288 columns as illustrated in FIG. 3. The number of "fonts" which can be displayed in the "TV-graphics mode" is 48 in the direction of row, and 16 in the direction of column. Also in this "TV-graphics mode", the subcode is formed so that the picture processing is performed by using a memory having addresses each of which corresponds to each pixel in a picture area having 50 "fonts" in the direction of row, and 18 "fonts" in the direction of column, made by adding a line of "fonts" to the upper and lower peripheries as well as the right and left outer peripheries of the "screen area".
As instructions for the picture processing, there is an instruction for painting out the whole picture area by one certain color, an instruction for drawing a picture in one "font" on the screen by using two different colors, an instruction for moving the whole picture upward, downward, or sideways, and so on.
Additionally, in the 8-bit groups forming the subcode, the Q bits forming the channel Q include time information corresponding to the track length to a certain position of each information data which is recorded from the beginning of the program area of CD, and form address time data which can be used as positional data representing the recording position. On the other hand, the P bits forming the channel P provide data including information relating to a pause between two music selections.
The system of recording and reproducing picture information as the subcode explained above is constructed so that as many as sixteen picture channels can be designated at maximum. Specifically, a "write font foreground/back-ground" instruction is used in the "TV-graphics mode", which has such a structure as illustrated in FIG. 4. This is an instruction for writing font data of the symbols 8 through 19 in positions having a row address defined by the symbol 6 and a column address defined by the symbol 7. For the pixels whose font data is "0", a color of a color number determined by the "color 0" is designated as a background color. For the pixels whose font data is "1", a color of a color number defined by "color 1" is designated as a foreground color. At the same time, sub-picture channels can be designated by using four bits of the channels R and S of the symbols 4 and 5. By this feature, as many as sixteen picture channels can be designated. Sixteen sorts of picture are previously recorded on a disc for example, and a desired picture channel can be selected on the playing side at the time of playing by this scheme of designating the picture channel.
In addition, there are numbers from "0" to "15" as color numbers. Sixteen colors indicated by the color number "0" through "15" are set by a "load CLUT color 0 through color 15 (load color look-up table color 0 through color 15)" instruction. The "load CLUT color 0 through color 15" instruction is an instruction having a structure illustrated in FIG. 7, and setting the contents of a color look-up table showing the color of pre-set color numbers or foreground/background color numbers. It is necessary to designate sixteen colors in total. However, since four bits are used respectively for each of RGB to indicate a color, two symbols are required for setting one color. Therefore, eight colors are set by one "pack" at most. With these circumstances, the instruction is divided into two instructions respectively designating eight colors of the first half, and eight colors of the second half.
The instruction code for the colors of the first half, i.e. the color 0 through the color 7, is determined to be "30", and the instruction code for the colors of the second half, i.e. the color 8 through color 15 are determined to be "31". The mixing of colors for each of the color numbers is as follows. Red color is represented by four bits of the channels R through U of even symbols allotted to the color number. Green color is represented by four bits, i.e. two bits of the channels V and W following the channels R through U of the even symbols, and two bits of the channels R and S of odd symbols. Blue color is represented by four bits of channels T through W following the channels R and S of the odd symbols. Therefore, 2.sup.4 (=16) sorts of gray scales are available for each color, and preparation of 16.sup.3 (=4096) colors is possible since three colors (RGB) are used. In addition, a gray scale "0000" corresponds to the darkest state, and a gray scale "1111" corresponds to the brightest state.
In the system of recording and reproducing picture information as the subcode as explained above, the time period necessary for displaying a picture of one "font" is about 3.3/1000 second, and about 2.5 seconds are necessary for displaying 48.times.16 characters. This means that picture information of an amount corresponding to a picture can not be obtained until the pickup traces the recording track for about 2.5 seconds. Therefore, in the case of recording medium playing apparatuses for playing a recording medium on which picture information is recorded as the subcode according to the conventional method, there has been a problem that disorder would be generated in the reproduced picture if a track jump operation is performed while picture information forming a picture is being read, in response to a command for a special reproduction operation such as a double speed reproduction operation which is performed by reproducing the recorded information in an order different from the order of recording, using the track jump operation for moving the information detection point of the pickup.
It to be noted that the "special reproduction operation" mentioned above does not include what is called a search operation, such as the chapter search operation.